Methods and apparatus for cleaning semiconductor wafers

ABSTRACT

A method for cleaning semiconductor substrate using ultra/mega sonic device comprising holding a semiconductor substrate by using a chuck, positioning a ultra/mega sonic device adjacent to the semiconductor substrate, injecting chemical liquid on the semiconductor substrate and gap between the semiconductor substrate and the ultra/mega sonic device, changing gap between the semiconductor substrate and the ultra/mega sonic device for each rotation of the chuck during the cleaning process. The gap can be increased or reduced by 0.5 /N for each rotation of the chuck, where λ is wavelength of ultra/mega sonic wave, N is an integer number between 2 and 1000. The gap is varied in the range of 0.5λn during the cleaning process, where λ is wavelength of ultra/mega sonic wave, and n is an integer number starting from 1.

FIELD OF THE INVENTION

The present invention generally relates to method and apparatus for cleaning semiconductor wafer. More particularly, relates to changing a gap between an ultra/mega sonic device and a wafer for each rotation of the wafer during the cleaning process to achieve an uniform ultra/mega sonic power density distribution on the wafer, which removes particles efficiently without damaging the device structure on the wafer.

BACKGROUND

Semiconductor devices are manufactured or fabricated on semiconductor wafers using a number of different processing steps to create transistor and interconnection elements. To electrically connect transistor terminals associated with the semiconductor wafer, conductive (e.g., metal) trenches, vias, and the like are formed in dielectric materials as part of the semiconductor device. The trenches and vias couple electrical signals and power between transistors, internal circuit of the semiconductor devices, and circuits external to the semiconductor device.

In forming the interconnection elements the semiconductor wafer may undergo, for example, masking, etching, and deposition processes to form the desired electronic circuitry of the semiconductor devices. In particular, multiple masking and plasma etching step can be performed to form a pattern of recessed areas in a dielectric layer on a semiconductor wafer that serve as trenches and vias for the interconnections. In order to removal particles and contaminations in trench and via post etching or photo resist aching, a wet cleaning step is necessary. Especially, when device manufacture node migrating to 65 nm and beyond, the side wall loss in trench and via during is crucial for maintaining the critical dimension. In order to reduce or eliminating the side wall loss, it is important to use moderate, dilute chemicals, or sometime de-ionized water only. However, the dilute chemical or de-ionized water usually is not efficient to remove particle in the trench and via. Therefore the mechanical force such as ultra sonic or mega sonic is needed in order to remove those particles efficiently. Ultra sonic and mega sonic wave will apply mechanical force to wafer structure, the power intensity and power distribution is key parameters to control the mechanical force within the damage limit and at the same time efficiently to remove the particles.

Mega sonic energy coupled with nozzle to clean semiconductor wafer is disclosed in U.S. Pat. No. 4,326,553. The fluid is pressurized and mega sonic energy is applied to the fluid by a mega sonic transducer. The nozzle is shaped to provide a ribbon-like jet of cleaning fluid vibrating at mega sonic frequencies for the impingement on the surface.

A source of energy vibrates an elongated probe which transmits the acoustic energy into the fluid is disclosed in U.S. Pat. No. 6,039,059. In one arrangement, fluid is sprayed onto both sides of a wafer while a probe is positioned close to an upper side. In another arrangement, a short probe is positioned with its end surface close to the surface, and the probe is moved over the surface as wafer rotates.

A source of energy vibrates a rod which rotates around it axis parallel to wafer surface is disclosed in U.S. Pat. No. 6,843,257 B2. The rod surface is etched to curve groves, such as spiral groove.

To uniformly apply right amount of mega sonic power to entire wafer is critical for the cleaning process. If the mega sonic power is not uniformly applied on the wafer, the portion of wafer receiving less mega sonic power will not be cleaned well, and leaving particles and contamination on the portion of the wafer, and portion of wafer receiving extra mega sonic power may cause the damage of device structure on the wafer.

It is needed to have a better method for controlling the mega sonic power density distribution on the wafer to clean particles and contamination on surface of wafer or substrate with higher efficiency and lower structure damages.

SUMMARY

One method of the present invention is to put a mega sonic device adjacent to front side of a rotating wafer during the cleaning process, and to increase the gap between the mega sonic device and the wafer for each rotation of the wafer. The increment of the gap for each rotation of the wafer is a friction of half wavelength of mega sonic wave, and the total increment of the gap is in the range of 0.5λN, where λ is the wavelength of mega sonic wave, and N is an integer number starting from 1.

Another method of the present invention is to put a mega sonic device adjacent to front side of a rotating wafer during the cleaning process, and to reduce the gap between the mega sonic device and the wafer for each rotation of the wafer. The reduction of the gap for each rotation of the wafer is a friction of half wavelength of mega sonic wave, and the total reduction of the gap is in the range of 0.5 λN, where λ is the wavelength of mega sonic wave, and N is an integer number starting from 1.

Another method of the present invention is to put a mega sonic device adjacent to back side of a rotating wafer, and to increase the gap between the mega sonic device and the wafer for each rotation of the wafer during the cleaning process. The increment of the gap for each rotation of the wafer is a friction of half wavelength of mega sonic wave, and the total increment of the gap is in the range of 0.5 λN, where

is the wavelength of mega sonic wave, and N is an integer number starting from 1.

Another method of the present invention is to put a mega sonic device adjacent to back side of a rotating wafer, and to reduce the gap between the mega sonic device and the wafer for each rotation of the wafer during the cleaning process. The reduction of the gap for each rotation of the wafer is a friction of half wavelength of mega sonic wave, and the total reduction of the gap is in the range of 0.5 λN, where

is the wavelength of mega sonic wave, and N is an integer number starting from 1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D depict an exemplary wafer cleaning apparatus;

FIG. 2 depicts an exemplary wafer cleaning process;

FIGS. 3A-3B depicts another exemplary wafer cleaning process;

FIG. 4 depicts another exemplary wafer cleaning apparatus;

FIG. 5 depicts a cleaning method;

FIG. 6 depicts another exemplary wafer cleaning apparatus;

FIG. 7 depicts another exemplary wafer cleaning apparatus;

FIG. 8 depicts another exemplary wafer cleaning apparatus;

FIG. 9 depicts another exemplary wafer cleaning apparatus;

FIGS. 10A-10G depicts variety of shape of ultra/mega sonic transducers.

DETAILED DESCRIPTION

FIGS. 1A to 1B show the conventional wafer cleaning apparatus using a mega sonic device. The wafer cleaning apparatus consists of wafer 1010, wafer chuck 1014 being rotated by rotation driving mechanism 1016, nozzle 1012 delivering cleaning chemicals or de-ionized water 1032, and mega sonic device 1003. The mega sonic device 1003 further consists of piezoelectric transducer 1004 acoustically coupled to resonator 1008. Transducer 1004 is electrically excited such that it vibrates and the resonator 1008 transmits high frequency sound energy into liquid. The agitation of the cleaning liquid produced by the mega sonic energy loosens particles on wafer 1010. Contaminants are thus vibrated away from the surfaces of the wafer 1010, and removed from the surfaces through the flowing liquid 1032 supplied by nozzle 1012.

As shown in FIG. 1C, in order to achieve the least reflection energy, the phase reflection wave r1 (from top of water film) must be opposite to reflection R2 (bottom of water film), therefore water film thickness must equal to:

d=nλ/2, n =1, 2, 3,. . .   (1)

Where, d is the thickness of water film or gap between mega-sonic device 1003 and wafer 1010, n is an integer number, and λ is wavelength of mega sonic wave in water. For example, for mega sonic frequency of 937.5 K Hz, λ=1.6 mm, the d =0.8 mm, 1.6 mm, 2.4 mm, and so on.

FIG. 1D shows the relationship between gap d and mega sonic power density measured by sensor 1002 as shown in FIG. 1A. Power density is varies from valley value 20 w/cm2 to peak value 80 w/cm2 as gap size increase 0.4 mm, and reach a full cycle in the gap increment of 0.8 mm (0.5λ). It is critical to maintain a gap precisely in order to keep a uniform mega sonic power distribution on the entire wafer.

However it is very difficult to keep a uniform gap in such precision in the reality, especially when the wafer is rotation mode. As shown in FIG. 2, if wafer chuck 1014 is set not 100% vertical to surface of mega sonic device 2003, the gap between mega sonic device and surface of wafer 2010 is reducing from edge of the wafer to center of the wafer. It will cause non uniform mega sonic power density distribution from edge of the wafer to center of the wafer according to data shown in FIG. 1D.

Another possible gap variation is caused by rotation axis of chuck being not veridical to surface of wafer 3010 as shown in FIGS. 3A and 3B. The wafer is wobbling when rotating, and FIG. 3B shows gap status after rotating 180 degree from status as shown in FIG. 3A. The gap at edge of wafer reduces from a biggest value as shown in FIG. 3A to smallest value as shown in FIG. 3B. It will cause non uniform mega sonic power density distribution on wafer as wafer passing mega sonic device. All such non uniform power distribution will either cause damage to device structure on the wafer and no uniformly cleaning wafer.

In order to overcome non uniform power distribution caused by variation of gap during chuck rotation, the present invention discloses a method as shown in FIG. 4. The gap between mega sonic device 4003 and wafer 4010 is increased or reduced by lead screw 4005 and motor 4006 as chuck 4014 rotating during cleaning process. Control unit 4088 is used to control the speed of motor 4006 based on speed of motor 4016. For each rotation of wafer 4010 or chuck 4014, control unit 4088 instructs motor 4006 to move mega sonic device 4003 up or down:

z=0.5λ/N   (2)

Where, λ is wavelength of ultra/mega sonic wave, and N is an integer number between 2 to 1000.

As shown further in detail in FIG. 5, when the gap increases for each rotation of wafer or chuck, the mega sonic power density at the same portion of wafer changes from P1 to P2. When the gap increases total half wavelength of mega sonic wave, the power density varies a full cycle from P1 to P11. The cycle starting point depends on the gap between mega sonic device and portion of wafer, however each portion on wafer will receive full cycle of power density when gap increases half wavelength of mega sonic wave. In other words, even gap between mega sonic device and wafer is not set uniformly due to reason described in FIG. 2, FIGS. 3A and 3B, each portion of the wafer will receive full cycle of mega sonic power when mega sonic device moves up half wavelength of mega sonic wave (about 0.8 mm for frequency of 937.5 kHz). This will guarantee each location of wafer to receive the same mount of mega sonic power density including the same average power density, the same maximum power density, and the same minimum power density. The operation sequence can be set as follows:

Process Sequence 1 (mega sonic frequency: f=937.5 kHz, and wavelength in dieonized water=λ=1.6 mm):

Step 1: rotating wafer at speed of ω, and ω is in the range of 10 rpm to 1500 rpm.

Step 2: move mega sonic device to adjacent to wafer with gap d, and d is in the range of 0.5 to 15 mm.

Step 3: turn on nozzle with deionized (DI) water or chemicals, and turn the mega sonic device on.

Step 4: for each rotation of chuck, move mega sonic device up 0.5λ/N (mm), where N is an integer number and in the range of 2 to 1000.

Step 5: continue step 4 until mega sonic device movies up total 0.5nλ (mm), where n is an integer number starting from 1.

Step 6: for each rotation of chuck, move mega sonic device down 0.5λ/N (mm), where N is an integer number and in the range of 2 to 1000 .

Step 7: continue step 6 until mega sonic device movies down total 0.5nλ (mm), where, n is an integer number starting form I.

Step 8: repeat step 4 to step 7 until wafer is cleaned.

Step 9: turn off mega sonic devices, stop the DI water or chemicals, and then dry the wafer.

Process Sequence 2 (mega sonic frequency: f =937.5 kHz, and wavelength in dieonized water=λ=1.6 mm):

Step 1: rotating wafer at speed of co, and co is in the range of 10 rpm to 1500 rpm.

Step 2: move mega sonic device to adjacent to wafer with gap d, and d is in the range of 0.5 to 15 mm.

Step 3: turn on nozzle with deionized (DI) water or chemicals, and turn the mega sonic device on.

Step 4: for each rotation of chuck, move mega sonic device up 0.5λ/N (mm), where N is an integer number and in the range of 2 to 1000.

Step 5: continue step 4 until mega sonic device movies up total 0.5nλ (mm), where n is an integer number starting form 1.

Step 6: turn off mega sonic devices, stop the DI water or chemicals, and then dry the wafer.

The frequency of transducer can be set at ultra sonic range and mega sonic range, depending on the particle to be cleaned. The larger the particle size is, the lower frequency should be used. Ultra sonic range is between 20 kHz to 200 kHz, and mega sonic range is between 200 kHz to 10 MHz. Also frequency of mechanical wave can be alternated either one at a time in succession or concurrently in order to clean different size of particles on the same substrate or wafer. If a dual frequency of waves are used, the higher frequency f₁ should be multiple integer number of lower frequency f₂, and the transducer moving range should be the 0.5λ₂n, increment or reduction of gap for each rotation of chuck should be 0.5λ₁/N, which λ₂ is wavelength of the wave with the lower frequency f₂, λ₁ is wavelength of the wave with the higher frequency f₁, and N is an integer number between 2 to 1000, and n is an integer number starting from 1.

One example of chemicals being used to remove the particle and contamination are shown as follows:

Organic Material Removal: H₂SO₄:H₂O₂=4:1

Particle Reduction: NH₄OH:H₂O₂:H₂O=1:1:5

Metal Contamination Removal: HCl:H₂O₂:H₂O=1:1:6

Oxide Removal: Oxide Removal=HF:H₂O=1:100

FIG. 6 shows another embodiment of wafer cleaning apparatus using a mega sonic device according to the present invention. The embodiment is similar to that shown in FIG. 4, except that chuck 6014 is moved vertically by lead screw 6005 and motor 6006. Control unit 6088 changes the gap d between mega sonic device 6003 and wafer 6010 by moving chuck 6014 up and down through lead screw 6005 and motor 6006.

FIG. 7 shows another embodiment of wafer cleaning apparatus using a mega sonic device according to the present invention. The embodiment is similar to that shown in FIG. 4, except that mega sonic device 7003 is placed adjacently to the back side of wafer 7010, and is moved vertically by lead screw 7005 and motor 7006. Control unit 7088 changes the gap d between mega sonic device 7003 and back side of wafer 7010 by moving mega sonic device 7003 up and down through lead screw 7005 and motor 7006. Mega sonic wave is transmitted to front side of wafer 7010 and water film 7032 through water film 7034 and wafer 7010. Nozzle 7011 supplies DI water or chemicals to maintain water film 7034 between mega sonic device 7003 and back side of wafer 7010. The advantage of this embodiment is to reduce or eliminate a possible damage caused by mega sonic wave to device structure on front side of wafer 7010.

FIG. 8 shows another embodiment of wafer cleaning apparatus using a mega sonic device according to the present invention. The embodiment is similar to that shown in FIG. 4, except that wafer 8010 is placed face down, and a nozzle array 8018 is placed underneath of front side of wafer 8010. Mega sonic wave is transmitted to front side of wafer 8010 through water film 8032 and wafer 8010 itself. A nozzle array 8018 sprays liquid chemicals or DI water on to front side of wafer 8010.

FIG. 9 shows another embodiment of wafer cleaning apparatus using a mega sonic device according to the present invention. The embodiment is similar to that shown in FIG. 4, except that surface of piezoelectric transducer 9004 has an angle a to surface of wafer 9010. Resonator 9008 is attached with piezoelectric transducer 9004, and mega sonic wave is transmitted to wafer through the resonator 9008 and DI water or chemical film 9032. Process sequence 1, 2, and 3 can be applied here.

FIGS. 10A to 10G show top view of mega sonic devices according to the present invention. Mega sonic device shown in FIG. 4 can be replaced by different shape of mega sonic devices 10003, i.e. triangle or pie shape as shown in FIG. 10A, rectangle as shown in FIG. 10B, octagon as shown in FIG. 10C, elliptical as shown in FIG. 10D, half circle as shown in FIG. 10E, quarter circle as shown in FIG. 10F, and circle as shown in FIG. 10G.

Although the present invention has been described with respect to certain embodiments, examples, and applications, it will be apparent to those skilled in the art that various modifications and changes may be made without departing from the invention. 

1. A method for a cleaning semiconductor substrate using ultra/mega sonic device, comprising: holding a semiconductor substrate by using a chuck; positioning a ultra/mega sonic device adjacent to the semiconductor substrate; injecting a chemical liquid onto the semiconductor substrate and into a gap between the semiconductor substrate and the ultra/mega sonic device by using at least one nozzle; providing a control unit, the control unit configured to execute a cleaning process, the cleaning process including injecting the chemical liquid onto the semiconductor substrate and into the gap using the at least one nozzle and changing the gap between the semiconductor substrate and the ultra/mega sonic, and wherein the control unit controls the speed of the chuck and changes the gap between the semiconductor substrate and the ultra/mega sonic device based on the value of a wavelength of the ultra/mega sonic wave in the cleaning liquid and the rotation of the chuck, and wherein during the cleaning process the control unit is configured to adjust the gap between the semiconductor substrate and the ultra/mega sonic device for each rotation of the chuck by 0.5λ/N until a total change of the gap is 0.5nλ, wherein λ is the wavelength of an ultra/mega sonic wave, N is an integer number between 2 to 1000, n is an integer number starting from 1, to provide a uniform power density application of the ultra/mega sonic device to the entire semiconductor substrate.
 2. The method of claim 1, wherein the gap is changed by moving ultra/mega sonic device in a direction vertical to the semiconductor substrate.
 3. The method of claim 1, wherein the gap is changed by moving the chuck in a direction vertical to the ultra/mega sonic device.
 4. The method of claim 1, wherein the ultra/mega sonic device is positioned adjacent to a front side of the semiconductor substrate.
 5. The method of claim 1, wherein the ultra/mega sonic device is positioned adjacent to a back side of the semiconductor substrate.
 6. The method of claim 5, wherein the chemical liquid is injected to the front side of the semiconductor substrate by the at least one nozzle placed adjacent to the front side of the semiconductor wafer, and the chemical liquid is injected to the backside of the semiconductor substrate by an another nozzle placed adjacent to the back side of semiconductor substrate.
 7. (canceled)
 8. (canceled)
 9. The method of claim 1, wherein the gap is varied in the range of 0.5λn during the cleaning process, where λ is a wavelength of the ultra/mega sonic wave, and n is an integer number starting
 1. 10. The method of claim 1, wherein sonic frequencies of the sonic device are dual frequencies.
 11. The method of claim 10, wherein the dual frequencies comprises a high frequency f1 and a low frequency f2,and f1=Mf2, where M is an integer number starting from
 2. 12. The method of claim 11, wherein the gap is reduced by 0.5λ1/N for each rotation of the chuck, where λ₁ is a wavelength of the wave with the high frequency f1,N is an integer number between 2 to
 1000. 13. The method of claim 11, wherein the gap is varied in the range of 0.5λn during the cleaning process, wherein λ is a wavelength of the wave with the low frequency f2,and n is an integer number starting from
 1. 14.-27. (canceled)
 28. The method of claim 6, wherein the chemical liquid is injected simultaneously on the front side and back side of the semiconductor wafer by the at least one nozzle and the another nozzle, respectively.
 29. A method for cleaning a semiconductor substrate using ultra/mega sonic device, comprising: holding a semiconductor substrate by using a chuck, the chuck connected to a motor; positioning a ultra/mega sonic device adjacent to the semiconductor substrate; injecting a chemical liquid onto the semiconductor substrate and into a gap between the semiconductor substrate and the ultra/mega sonic device by using at least one nozzle; providing a control unit, the control unit configured to execute a cleaning process, the cleaning process including injecting the chemical liquid onto the semiconductor substrate and into the gap using the at least one nozzle and changing the gap between the semiconductor substrate and the ultra/mega sonic device, and wherein the control unit controls the speed of the chuck and changes the gap between the semiconductor substrate and the ultra/mega sonic device based on the value of a wavelength of the ultra/mega sonic wave in the cleaning liquid and the rotation of the chuck.
 30. The method of claim 29, wherein the gap is changed by moving ultra/mega sonic device in a direction vertical to the semiconductor substrate.
 31. The method of claim 29, wherein the gap is changed by moving the chuck in a direction vertical to the ultra/mega sonic device.
 32. The method of claim 29 wherein the ultra/mega sonic device is positioned adjacent to a front side of the semiconductor substrate.
 33. The method of claim 29, wherein the ultra/mega sonic device is positioned adjacent to a back side of the semiconductor substrate.
 34. The method of claim 33, wherein the chemical liquid is injected to the front side of the semiconductor substrate by the at least one nozzle placed adjacent to the front side of the semiconductor wafer, and the chemical liquid is injected to the backside of the semiconductor substrate by a another nozzle placed adjacent to the back side of semiconductor substrate.
 35. The method of claim 1, wherein the gap is varied in the range of 0.5λn during the cleaning process, where λ is a wavelength of the ultra/mega sonic wave, and n is an integer number starting
 1. 36. The method of claim 1, wherein sonic frequencies of the sonic device are dual frequencies. 